1. Su le spectre des operateurs elliptiques a bicharacteristiques toutes periodiques;de Verdière;Comment. Math. Helv.,1979
2. The spectrum of positive elliptic operators and periodic geodesics;Duistermaat;Invent. Math.,1975
3. Some spectral results for the Laplace operator with potential on the n-sphere;Guillemin;Adv. in Math.,1978
4. The Radon transform on Zoll surfaces;Guillemin;Adv. in Math.,1976
5. On the spectra of commuting pseudodifferential operators: Recent work of Kac-Spencer, Weinstein and others;Guillemin,1979